To determine the size of your copper pipe, you'll need to measure its outside diameter (OD) and then use a conversion to determine the nominal pipe size. Here's how:
Measuring the Copper Pipe
You can use a few different tools to measure the outside diameter of your copper pipe:
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Ruler or Measuring Tape: This is suitable if the end of the pipe is exposed. Place the ruler or tape measure across the diameter of the pipe. Try to be as accurate as possible.
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Soft Tape Measure: Wrap the tape measure around the circumference of the pipe and divide that measurement by pi (approximately 3.14159) to get the outside diameter.
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Caliper: This is the most accurate method. Place the caliper jaws around the outside of the pipe and take the measurement. Digital calipers are even more precise.
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Pipe Caliper (Optional): A specialized pipe caliper has markings that directly indicate common iron or copper pipe sizes, making the process easier.
Understanding Nominal Pipe Size (NPS)
It's crucial to understand that the nominal pipe size doesn't directly correspond to the actual outside diameter. Copper pipe sizes are referred to by their nominal size, which is a rough approximation. The actual OD will be slightly larger.
Conversion Chart and Example
Once you have the outside diameter, you can use a chart like the one below to find the corresponding nominal pipe size:
| Nominal Pipe Size (NPS) | Actual Outside Diameter (OD) |
|---|---|
| 1/2" | 5/8" (0.625") |
| 3/4" | 7/8" (0.875") |
| 1" | 1 1/8" (1.125") |
| 1 1/4" | 1 3/8" (1.375") |
| 1 1/2" | 1 5/8" (1.625") |
| 2" | 2 1/8" (2.125") |
Example:
Let's say you measure the outside diameter of your copper pipe and it's approximately 0.875 inches (7/8"). According to the chart, this corresponds to a nominal pipe size of 3/4".
Important Considerations:
- Type of Copper: Different types of copper pipe (like Type K, Type L, and Type M) have the same outside diameter for a given nominal size, but they have different wall thicknesses, affecting the inside diameter and pressure rating. Knowing the type of copper is important for choosing the correct fittings.
- Fittings: Always use fittings that are compatible with the type and size of copper pipe you have.
By accurately measuring the outside diameter of your copper pipe and consulting a conversion chart, you can easily determine its nominal size for plumbing projects and repairs.
